The removal of solid particles such as dust suspended in a primary gaseous stream by means of electrostatic precipitation is a well-known art. A high electrical potential is established across two spaced electrodes between which the dust-laden gas flows. A corona discharge is established at the emitter electrode due to the voltage gradient which produces an ion cloud that brings about a surface attachment of ions to the solid particles suspended in the primary gas.
By virtue of the electrostatic field extending between the electrodes, the charged solid particles are attracted toward the collector electrode surface. If the particles are of low resistivity they may become neutralized upon contacting the collector electrode. Despite this neutralization the particles tend to be retained on the collector surface by virtue of other forces such as cohesion and adhesion as well as induced electrostatic forces due to the incoming ion shower.
Modern industrial precipitators take several different forms. The parallel flat plate collector electrodes with multiple wire emitters or discharge electrodes are common. In another design the emitter wires are replaced by an open grid. Special designs may employ a circular collector tube with an axial wire emitter. In all electrostatic precipitators there exists the problem of cleaning the particulate layer from the collector surface.
It has now become cnventional to clean the solid particulate layer from the collector plate electrodes by means of vibrationally rapping or jarring the collector surfaces. The detached layer, in a more or less agglomerated sense, falls to the hoppers or bins below. In falling along side of the collector electrode surface the fractured layer tends to further break up and disperse. Most of the dust falls to the hoppers below, but a significant portion of this dispersed material becomes reentrained in the primary gas flowing through the electrostatic precipitator and is thus discharged at the outlet. To minimize this effect it is common to place multiple collector electrode assemblies in series along the flow path to cope with the particulate reentrainment problem. As a result, electrostatic precipitator devices have become physically very large.